Ultra high strength body and chassis components

ABSTRACT

A structural component for an automotive vehicle formed from a single-piece of steel material and having a closed, complex cross-section with increased strength, for example a strength of greater than 650 MPa, and thus improved performance, is provided. The structural component typically has an elongation of greater than 5%. The structural component is formed by expanding a boron-containing steel material, for example heating or hydroforming a tube of the steel material. The boron-containing steel material expands by least 2% during the forming process and thus achieves the closed, complex cross-section, while also achieving the high strength. In addition, the structural component can be formed with zones of varying thickness, strength, hardness, elongation, and/or other varying properties to achieve the desired performance.

CROSS REFERENCE TO RELATED APPLICATIONS

This PCT Patent Application claims the benefit of U.S. ProvisionalPatent Application Ser. No. 62/194,429 filed on Jul. 20, 2015 entitled“Ultra High Strength Body And Chassis Components,” the entire disclosureof the application being considered part of the disclosure of thisapplication and hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates generally to structural components for automotivevehicles, more particularly to high strength body and chassis componentsformed of steel, and methods of manufacturing the same.

2. Related Art

High strength structural components formed of steel for automotivevehicles, such as rails, beams, and pillars of the vehicle body orchassis, are oftentimes formed with complex closed cross-sections, forexample cross-sections which vary in shape and/or thickness. A highstrength component is typically required when used in a vehicle body orchassis application. In addition, the strength, elongation, or anothermaterial property is oftentimes varied along the length of the componentto enhance performance. For example, the component can include a firstzone having a high strength, and a second zone having a high ductility.

One process currently used to produce a component formed of steel andhaving a complex cross-section includes forming a first part with aU-shaped cross-section, forming a second part with a U-shapedcross-section, and then welding the first part to the second part toprovide a tubular cross-section. Hydroforming is another process used toform a steel component having a complex cross-section, for example aclosed cross-section having a shape which varies along the length of thecomponent. This process includes disposing a tube of the steel materialbetween two dies of a hydroforming press, closing the dies, andinjecting high pressure water into the ends of the tube such that thetube expands and conforms to the shape of the dies. However, the currenthydroforming process is limited to use with low carbon steel, which hasa low expansion during the forming process and a limited strength. Aprocess for forming a steel component having a closed, complex, orvarying cross-section with higher strength is desired.

SUMMARY OF THE INVENTION

The invention provides a method of manufacturing a structural componenthaving a closed, complex, or varying cross-section with higher strength.The method includes providing a tube surrounding a hollow opening andextending between opposite ends, wherein the tube is formed of a steelmaterial including boron; and expanding the steel material.

The invention also provides the structural component comprising a steelmaterial surrounding a hollow opening and extending between oppositeends, wherein the steel material contains boron, and a cross-section ofthe steel material varies between the opposite ends.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1A illustrates a comparative front or rear rail for an automotivevehicle having a closed cross-section and formed by joining two piecesof steel material without boron;

FIG. 1B illustrates a front or rear rail for an automotive vehiclehaving a closed cross-section formed by expanding a single-piece ofboron-containing steel material according to a first example embodimentof the invention;

FIG. 2A illustrates a comparative front or rear frame rail for anautomotive vehicle having a closed cross-section and formed by joiningtwo pieces of steel material without boron:

FIG. 2B illustrates a front or rear frame rail for an automotive vehiclehaving a closed cross-section formed by expanding a single-piece ofboron-containing steel material according to a second example embodimentof the invention;

FIG. 3A illustrates a comparative front end shotgun structure for anautomotive vehicle formed from a steel material without boron;

FIG. 3B illustrates a front end shotgun structure for an automotivevehicle having a closed cross-section formed by expanding a single-pieceof boron-containing steel material according to a third exampleembodiment of the invention;

FIG. 4A illustrates a comparative B-pillar for an automotive vehiclehaving a closed cross-section and formed by joining two pieces of steelmaterial without boron;

FIG. 4B illustrates a B-pillar for an automotive vehicle having a closedcross-section formed by expanding a single-piece of boron-containingsteel material according to a fourth example embodiment of theinvention;

FIG. 5A illustrates a comparative roof rail for an automotive vehiclehaving a closed cross-section and formed from a steel material withoutboron;

FIG. 5B illustrates a roof rail for an automotive vehicle having aclosed cross-section formed by expanding a single-piece ofboron-containing steel material according to a fifth example embodimentof the invention;

FIG. 6A illustrates a comparative rail for an automotive vehicle havinga closed cross-section and formed by joining two pieces of steelmaterial without boron; and

FIG. 6B illustrates a rail for an automotive vehicle having a closedcross-section formed by expanding a single-piece of boron-containingsteel material according to a sixth example embodiment of the invention;

DESCRIPTION OF THE EXAMPLE EMBODIMENTS

The invention provides an ultra-high strength structural component 20for an automotive vehicle having a closed, complex cross-section formedby heating and expanding a single-piece of steel material. The steelmaterial contains boron which provides the high strength and anexpansion of 2% to 50% during the forming process. The structuralcomponent 20 can be used in various automotive vehicle applications,such as body or chassis applications. For example the structuralcomponent 20 can be used as a rail, beam, pillar, or frame. Examplestructural components 20 which can be formed according to embodiments ofthe invention, for example to replace the structural components of FIGS.1A-6A, are shown in FIGS. 1B-6B.

The structural component 20 is formed from a boron-containing orboron-based steel material, for example medium or high carbon steelalloyed with boron. The steel material is typically iron-based, orcontains iron in an amount greater than the individual amount, orpossibly the total amount, of every other element present in the steelmaterial. Medium and high carbon steels are typically preferred forautomotive vehicle applications compared to low carbon steel due to thehigher strength. Various boron-containing compositions can be used toform the structural component 20, for example 22MnB5 steel, 30MnB5steel, 38MnB5 steel, or steel of the xxBxx series. The steel material istypically a boron-alloyed quenched and tempered steel.

When the steel material is 22MnB5 steel, the composition of the steelmaterial can include carbon in an amount of 0.19 to 0.25 percent byweight (wt. %), silicon in an amount up to 0.40 wt. %, manganese in anamount of 1.10 to 1.40 wt. %, phosphorous in an amount up to 0.025 wt.%, sulfur in an amount up to 0.015 wt. %, aluminum in an amount up to0.08 wt. %, nitrogen in an amount up to 0.01 wt. %, chromium in anamount up to 0.30 wt. %, and boron in an amount of 0.0008 to 0.0050 wt.%, based on the total weight of the steel material.

When the steel material is 30MnB5 steel, the composition of the steelmaterial can include carbon in an amount of 0.27 to 0.32 percent byweight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese inan amount of 1.15 to 1.40 wt. %, phosphorous in an amount up to 0.023wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount upto 0.080 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in anamount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045wt. %, and boron in an amount of 0.0015 to 0.0040 wt. %, based on thetotal weight of the steel material.

When the steel material is 38MnB5 steel, the composition can includecarbon in an amount of 0.36 to 0.40 percent by weight (wt. %), siliconin an amount of 0.15 to 0.35 wt. %, manganese in an amount of 1.20 to1.40 wt %, phosphorous in an amount up to 0.020 wt. %, sulfur in anamount up to 0.010 wt. %, aluminum in an amount up to 0.060 wt. %,nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boronin an amount of 0.0015 to 0.0045 wt. %, based on the total weight of thesteel material.

According to one example embodiment, the structural component 20 isformed by providing a tube of the steel material, heating the tube, andexpanding the tube to achieve the structural component 20 having thedesired complex or varying cross-sectional shape along its length. Theheating step typically includes heating the tube to a temperature of 900to 950° C. During the expansion step, at least one dimension of the tubeincreases by 2% to 50%. For example, the diameter, width, length, and/orheight of the tube can increase by at least 2%. The structural component20 formed typically has a width extending across a center axis A whichvaries along the length of the component 20. The cross-sectional shapeachieved can be referred to as closed and non-circular, tubular, orO-shaped.

The boron-containing steel material is able to flow better when heated,compared to in colder states. The boron-containing steel material has anexpansion of at least 2% or greater than 2%, typically greater than 10%,and up to 50% when heated to a temperature greater than 400° C. Thepresence of boron in the steel material allows for the formation ofcomplex or varying cross-sectional shapes, even when the steel materialhas a medium or high carbon content. The expansion of at least 2% is animprovement over the expansion achieved by other steel materials whichhave been used in an expansion forming process, such as low carbonsteels without boron. The steel material used to form the comparativestructural components of FIGS. 1A-6A, for example, has an expansion ofless than 2% during the forming process when heated to the sametemperature. Thus, to achieve the complex, closed cross-section, twoseparate pieces of the comparative steel material need to be laserwelded or otherwise joined together.

The boron-containing steel material used to form the single-piecestructural components 20 of FIGS. 1B-6B also provides a yield strengthof greater than 550 MPa and a tensile strength of greater than 650 MPaafter the expansion process. The strength provided by theboron-containing steel material after the expansion process is animprovement over the comparative steel materials without boron, whichprovide a yield strength of less than 550 MPa and a tensile strength ofless than 650 MPa after the expansion process.

In another example embodiment, a hydro-forming process is used to formthe structural component 20. This process typically includes disposingthe tube of boron-containing steel material between two dies of ahydroforming press, closing the dies, and injecting high pressure waterinto the ends of the tube such that the tube expands and conforms to theshape of the dies. The hydroforming press is typically a low tonnagepress. The shape of the dies is designed to achieve the complexcross-sectional shape along the length of the structural component 20.Alternatively, another type of forming process which includes expandingthe boron-containing steel material can be used to obtain the desiredshape.

In addition to a cross-sectional shape which varies along the length ofthe component 20, the structural component 20 can also have a varyingthickness along its length. For example, the example structuralcomponent 20 of FIG. 1B is formed with a first zone 26 extending from afirst end 22 toward a second end 24 which has a greater thickness than asecond zone 28 extending from the first zone 26 to a second end 24.Varying the thickness along the length of the component 20 can reduceweight and achieve properties which enhance performance of thestructural component 20.

The structural component 20 can also be formed to have a homogenous orvarying hardness, strength, elongation, ductility, and/or anothervarying property along its length. For example, the first zone 26 canhave a higher strength and hardness than the second zone 28, and thesecond zone 28 can have a higher elongation and ductility. A yieldstrength of greater than 550 MPa, a tensile strength of greater than 650MPa, and an elongation of greater than 5% can be achieved using theboron-containing steel material. Thus, the structural component 20 canbe referred to as an ultra-high strength component.

The varying hardness, strength, elongation, and/or ductility along thelength of the structural component 20 can be achieved by coolingdifferent zones of the structural component 20 at different rates afterthe heating and/or forming steps. For example, the first zone 26 of thestructural component 20 can be cooled to room temperature or belowfaster than the second zone 28

As alluded to above, the structural component 20 of the first exampleembodiment shown in FIG. 1B can be used in place of the comparativestructural component shown in FIG. 1A. In this embodiment, thecomparative structural component is formed by welding two pieces ofsteel material without boron together to achieve the closedcross-section. The structural component 20 of the first exampleembodiment shown in FIG. 1B is formed by heating and expanding a singlepiece of boron-containing steel material to achieve the closed andvarying cross-section. The boron-containing steel material has anexpansion of at least 2% during the forming process. In addition, theexample structural component 20 is formed with the first zone 26 havinga higher hardness and strength, for example, a yield strength of 500 MPato 1500 MPa, and the second zone 28 having a higher ductility andelongation. Alternatively, the structural component 20 could have ahomogenous yield strength of 500 MPa to 1500 MPa and an expansion ofgreater than 2%. In addition to being formed with a variablecross-section and strength, the structural component 20 can be formedwith a variable thickness, for example a lower thickness along thesecond zone 28 to reduce weight. The structural components of FIGS. 1Aand 1B are typically used as a front or rear rail for an automotivevehicle.

FIGS. 2B-6B illustrate other example structural components 20 which canbe used in place of the structural components shown in FIGS. 2A-6A. Thestructural component 20 of the second example embodiment shown in FIG.2B can be used in place of the comparative structural component shown inFIG. 2A. In this embodiment, the comparative structural component isformed by welding two pieces of steel material without boron together toachieve the closed cross-section. The structural component 20 of thesecond example embodiment shown in FIG. 2B is formed by heating andexpanding a single tube of boron-containing steel material to achievethe closed and varying cross-section. The boron-containing steelmaterial has an expansion of at least 2% during the forming process. Inaddition, the example structural component 20 is formed with severalfirst zones 26 having a higher hardness and strength, for example ayield strength of 650 MPa to 2000 MPa, and two second zones 28 having alower strength but higher ductility and elongation, for example anelongation of greater than 5%. The first zones 26 could have a strength,elongation, and other properties the same as or different from oneanother. The two second zones 28 could also have a strength, elongation,and other properties the same as or different from one another.Alternatively, the structural component 20 can be formed with ahomogenous strength, hardness, ductility, and/or elongation along itslength, for example a yield strength of 650 MPa to 2000 MPa, or 950 MPato 2000 MPa, and an elongation of greater than 5%. The structuralcomponents of FIGS. 2A and 2B are typically used as a front or rearframe rail for an automotive vehicle.

The structural component 20 of the third example embodiment shown inFIG. 3B can be used in place of a comparative structural componentformed using the part shown in FIG. 3A. In this embodiment, thecomparative structural component is formed by welding two of the partsof steel material without boron together to achieve the closedcross-section. If the comparative structural component of FIG. 3A isformed by an expansion process, then the comparative structuralcomponent has a limited expansion and/or limited strength. Thestructural component 20 of the third example embodiment shown in FIG. 3Bis formed by heating and expanding a tube of boron-containing steelmaterial to achieve the closed and varying cross-section. Theboron-containing steel material has an expansion of at least 2% duringthe forming process. This example structural component 20 also has ayield strength 700 MPa to 2000 MPa, for example 780 MPa or greater, andan elongation of greater than 5%, for example around 10% or greater. Thestructural components of FIGS. 3A and 3B are typically used as a frontend shotgun structure for an automotive vehicle. The properties andshape of the example structural component 20 provide for narrow offsetin the event of a crash.

The structural component 20 of the fourth example embodiment shown inFIG. 4B can be used in place of the comparative structural componentshown in FIG. 4A. In this embodiment, the comparative structuralcomponent is formed by welding two pieces of steel material withoutboron together to achieve the closed cross-section. The structuralcomponent 20 of the fourth example embodiment shown in FIG. 4B is formedby heating and expanding three pieces of boron-containing steel materialtogether to achieve the closed cross-section, and then tailor weldingthe three pieces together. The boron-containing steel material has anexpansion of at least 2% during the forming process. The three piecesprovide two first zones 26 having a higher strength spaced from oneanother by a second zone 28 having a lower strength. The first zones 26have a tensile strength of 980 MPa to 2000 MPa, and the second zone hasa tensile strength of 610 MPa to 980 MPa. The three pieces also havedifferent cross-sectional shapes. During the tailor welding process,transition zones 30 are formed between the different zones. The tailorwelding process also provides a varying thickness along the length ofthe structural component 20. The structural components of FIGS. 4A and4B are typically used as a B-pillar along the side body of an automotivevehicle.

The structural component 20 of the fifth example embodiment shown inFIG. 5B can be used in place of the comparative structural componentshown in FIG. 5A. In this embodiment, the comparative structuralcomponent is formed by expanding a tube of steel material without boronto achieve the closed cross-section. However, in this case, theexpansion provided by the steel material without boron is limited toaround or below 2%. The structural component 20 of the fifth exampleembodiment shown in FIG. 5B is formed by heating and expanding a tube ofboron-containing steel material to achieve the closed and varyingcross-section. The boron-containing steel material has an expansion ofat least 3% during the forming process. The material located in thecenter of the structural component 20 has an expansion of up to 30%.This example structural component 20 also achieves a yield strength 980MPa to 2000 MPa and an elongation of greater than 5%. The structuralcomponents of FIGS. 5A and 5B are typically used as a roof rail of anautomotive vehicle.

The structural component 20 of the sixth example embodiment shown inFIG. 6B can be used in place of the comparative structural componentshown in FIG. 6A. In this embodiment, the comparative structuralcomponent is formed by welding two pieces of steel material withoutboron together to achieve the closed cross-section. If the structuralcomponent of FIG. 6A is formed by an expansion process, then thecomparative structural component has a limited expansion and/or limitedstrength. The structural component 20 of the sixth example embodimentshown in FIG. 6B is formed by heating and expanding a single tube ofboron-containing steel material to achieve the closed cross-section. Theboron-containing steel material has an expansion of at least 2% duringthe forming process. This example structural component 20 also achievesa yield strength 700 MPa to 2000 MPa, for example 1500 MPa, and anelongation of greater than 5%. The structural components of FIGS. 6A and6B are typically used as a beam for an automotive vehicle. Thecomponents of FIGS. 6A and 6B are also formed with holes to reduceweight.

Many modifications and variations of the present disclosure are possiblein light of the above teachings and may be practiced otherwise than asspecifically described while within the scope of the claims.

1. A method of manufacturing a structural component, comprising thesteps of: providing a tube surrounding a hollow opening and extendingbetween opposite ends, the tube being formed of a steel materialincluding boron; and expanding the steel material.
 2. The method ofclaim 1, wherein the expanding step includes disposing the tube betweena pair of dies and injecting water under pressure into the hollowopening of the tube.
 3. The method of claim 1, wherein the expandingstep includes heating the steel material to a temperature greater than400° C.
 4. The method of claim 1, wherein the steel material expands byat least 2% when heated to a temperature greater than 400° C. or whenthe hollow opening is filled with water under pressure.
 5. The method ofclaim 1, wherein the steel material expands by greater than 10% and upto 50% when heated to a temperature greater than 400° C. or when thehollow opening is filled with water under pressure.
 6. The method ofclaim 1, wherein the expanding step includes increasing the area of thecross-sectional opening between the opposite ends.
 7. The method ofclaim 1, wherein the expanding step includes varying the thickness ofthe tube between the opposite ends.
 8. The method of claim 1, whereinthe steel material of at least one zone of the tube has a yield strengthof greater than 550 MPa and a tensile strength of greater than 650 MPaafter the expanding step.
 9. A structural component, comprising: a steelmaterial surrounding a hollow opening and extending between oppositeends; the steel material containing boron; and a cross-section of thesteel material varying between the opposite ends.
 10. The structuralcomponent of claim 9, wherein the steel material has a yield strength ofgreater than 550 MPa and a tensile strength of greater than 650 MPa. 11.The structural component of claim 9, wherein at least one of thethickness of the structural component and the cross-sectional area ofthe hollow opening varies between the opposite ends.
 12. The structuralcomponent of claim 9, wherein at least one of the strength, hardness,elongation, and ductility of the structural component varies between theopposite ends.
 13. The structural component of claim 9, wherein thesteel material includes carbon in an amount of 0.19 to 0.25 percent byweight (wt. %), silicon in an amount up to 0.40 wt. %, manganese in anamount of 1.10 to 1.40 wt. %, phosphorous in an amount up to 0.025 wt.%, sulfur in an amount up to 0.015 wt. %, aluminum in an amount up to0.08 wt. %, nitrogen in an amount up to 0.01 wt. %, chromium in anamount up to 0.30 wt. %, and boron in an amount of 0.0008 to 0.0050 wt.%, based on the total weight of the steel material.
 14. The structuralcomponent of claim 9, wherein the steel material includes carbon in anamount of 0.27 to 0.32 percent by weight (wt. %), silicon in an amountof 0.15 to 0.35 wt. %, manganese in an amount of 1.15 to 1.40 wt. %,phosphorous in an amount up to 0.023 wt. %, sulfur in an amount up to0.010 wt. %, aluminum in an amount up to 0.080 wt. %, nitrogen in anamount up to 0.010 wt. %, chromium in an amount of 0.10 to 0.25 wt. %,titanium in an amount of 0.015 to 0.045 wt. %, and boron in an amount of0.0015 to 0.0040 wt. %, based on the total weight of the steel material.15. The structural component of claim 9, wherein the steel materialincludes carbon in an amount of 0.36 to 0.40 percent by weight (wt. %),silicon in an amount of 0.15 to 0.35 wt. %, manganese in an amount of1.20 to 1.40 wt. %, phosphorous in an amount up to 0.020 wt. %, sulfurin an amount up to 0.010 wt. %, aluminum in an amount up to 0.060 wt. %,nitrogen in an amount up to 0.010 wt. %, chromium in an amount of 0.10to 0.25 wt. %, titanium in an amount of 0.015 to 0.045 wt. %, and boronin an amount of 0.0015 to 0.0045 wt. %, based on the total weight of thesteel material.
 16. The method of claim 1, wherein at least one of thethickness of the structural component and the cross-sectional area ofthe hollow opening varies between the opposite ends.
 17. The method ofclaim 1, wherein at least one of the strength, hardness, elongation, andductility of the structural component varies between the opposite ends.18. The method of claim 1, wherein the steel material includes carbon inan amount of 0.19 to 0.25 percent by weight (wt. %), silicon in anamount up to 0.40 wt. %, manganese in an amount of 1.10 to 1.40 wt. %,phosphorous in an amount up to 0.025 wt. %, sulfur in an amount up to0.015 wt. %, aluminum in an amount up to 0.08 wt. %, nitrogen in anamount up to 0.01 wt. %, chromium in an amount up to 0.30 wt. %, andboron in an amount of 0.0008 to 0.0050 wt. %, based on the total weightof the steel material.
 19. The method of claim 1, wherein the steelmaterial includes carbon in an amount of 0.27 to 0.32 percent by weight(wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganese in anamount of 1.15 to 1.40 wt. %, phosphorous in an amount up to 0.023 wt.%, sulfur in an amount up to 0.010 wt. %, aluminum in an amount up to0.080 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in anamount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045wt. %, and boron in an amount of 0.0015 to 0.0040 wt. %, based on thetotal weight of the steel material.
 20. The method of claim 1, whereinthe steel material includes carbon in an amount of 0.36 to 0.40 percentby weight (wt. %), silicon in an amount of 0.15 to 0.35 wt. %, manganesein an amount of 1.20 to 1.40 wt. %, phosphorous in an amount up to 0.020wt. %, sulfur in an amount up to 0.010 wt. %, aluminum in an amount upto 0.060 wt. %, nitrogen in an amount up to 0.010 wt. %, chromium in anamount of 0.10 to 0.25 wt. %, titanium in an amount of 0.015 to 0.045wt. %, and boron in an amount of 0.0015 to 0.0045 wt. %, based on thetotal weight of the steel material.